OLENEKIAN (EARLY TRIASSIC) FOSSIL ASSEMBLAGE FROM EASTERN JULIAN ALPS (SLOVENIA)

摘要

The deposition of red and variegated mudstones and claystones characterized the ancient Tethys Ocean during Cretaceous and Palaeogene times, including in its north-western part, the Alpine–Carpathian deep-water basins. Palaeogene variegated sediments, containing red mudstone and claystone layers, crop out in the Gorce Mountains (Rosocha creek, near Lubomierz) in the Magura Nappe (Bystrica Subunit) of the Polish Outer Carpathians. These sediments occur as layers 1–10 cm thick and as packages of layers 2–3 m thick that are associated with very thin-bedded turbidites. The entire succession is tectonically disturbed and parts of it belong to the Ropianka, abowa Shale and Belovea Formations. The sediments studied contain 27 genera and 59 species that belong to deep-water agglutinated foraminiferal (DWAF) assemblages. Tubular taxa, which are frequent in various Mesozoic–Cenozoic flysch sediments are relatively rare in the section studied. The assemblages are moderately diverse (3–20 taxa per sample). Excluding tubular forms, the most common taxa belong to Trochamminoides – Paratrochamminoides spp., Saccammina placenta , glomospirids, Recurvoides – Recurvoidella spp. and karrerulinids. The oldest part of the red sediments, referable to the Ropianka Formation, represents the upper part of the Rzehakina fissistomata Zone (probably the Upper Palaeocene). The youngest red sediments, forming thin intercalations in the Belovea Formation, represent the acme of Reticulophragmium amplectens (middle Lutetian). Owing to tectonic disturbances, most of the Lower Eocene part of the variegated facies of the abowa Shale Formation is not preserved in the section studied. The upper part of it, a package 2 m thick, represents the lower part of the Reticulophragmium amplectens Zone. The small thickness (10–15 m) of the abowa Shale Formation in the section studied is similar to other sections in the southern part of the Bystrica Subunit. It is probably of a sedimentary nature, reflecting a decreasing number of mud-rich, gravitational flows in the southern part of the Magura Basin during the Early Eocene. Nevertheless, the strong tectonic disturbances that took place in this area during the Oligocene–Miocene folding and overthrusting influenced the reduction in thickness of these sediments.